Reducing weight in cars is a win-win for everyone

An employee of German luxury car maker Porsche working on the Porsche 911 sportcar assembly line at their plant in Stuttgart, southwestern Germany.

PHOTO: THOMAS KIENZLE, AFP/Getty Images

By Graeme Fletcher, Postmedia News

Originally published: August 22, 2013

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MEDIUM

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Heading into the future, more manufactures are going to be shedding kilograms in an effort to reduce fuel consumption. According the U.S. Energy Department, a 10% reduction in vehicle mass equates to a fuel consumption reduction of 6% to 8%. That, by any measure, is a very good return on investment. As David Booth noted recently, Ford is looking at putting more aluminum into the F-150 pickup and Jaguar is planning to extend its use of aluminum in future products.

The lightweight thrust is coming in many forms. First, there’s good old steel. As the blend of steel has changed in recent years, it is now is up to five times stronger than the steel from a decade ago. As a result, something that once weighed 45 kilograms can be replaced with an ultra-high strength steel component that’s 10 kg lighter without affecting overall cost. This represents an enormous step forward, but more is going to have to happen if mass reduction is to have a positive effect. This is where aluminum and other exotic materials are beginning to make in-roads.

Audi has long been using exotic materials to build its vehicles. Way back when the world was in the process of warming, August Horch (one of Audi’s four rings) used an alloy crankcase and gearbox housing in the 1903 Horch Tonneau. However, the modern lightweight revolution started with the Audi A8 and its Audi Space Frame (ASF), which was introduced in 1994. The A8’s ASF tipped the scales at a mere 249 kg, which represented a whopping mass reduction of 200 kg when compared to the same thing built of steel.

Audi then set about finding a solution to the cost of using an all-aluminum frame — aluminum is expensive and while often used in high-end cars, its use in everyday runabouts has, until now, been very limited. The solution is found in the latest A6 — the body is a steel/aluminum hybrid. The core structure is made of high-strength/ultra-high steel, however, where practical, large, typically heavier, components are made of aluminum. In this case, the front suspension towers, front fenders, hood, deck lid and doors. Even the rear parcel shelf rides on an aluminum bulkhead. In the end, it means that 20% of the A6 is constructed of this lightweight material.

The advantage is simple: The steel/aluminum hybrid construction delivers a body with a 50% improvement in rigidity, yet it drops the mass by 15% when compared to an all-steel unit. As a result, the 2013 A6 is 80 kg lighter than the previous model in spite of having increased content, a host of new features and improved levels of safety.

Moving forward, aluminum is going to be replaced by carbon-fibre reinforced plastic (CFRP). It is 50% lighter than steel, 30% lighter than aluminum, yet it is as strong as either, which is an important consideration in crash safety. For now, the extensive use of CFRP remains the exclusive domain of truly exotic and otherworldly cars like the Lamborghini Aventador. It uses carbon fibre in the passenger cell and then bolts on aluminum front and rear sections to support the running gear and sundry other add-ons needed to produce a true supercar. One of the key advantages to this is that the aluminum front and rear is readily repaired — CFRP is still tough to fix without replacing the entire structure.

BMW is set to bring the use of CFRP down to the everyday level when the i3 arrives next year. It is the start of an adventurous journey that will ultimately introduce the world to the first plug-in hybrid supercar — the seductive i8.

The i3 is an all-electric urban commuter car that uses aluminum for the core structure with a CFRP safety cell for the passengers. When it is equipped with its range-extender (a small gasoline-powered engine), it delivers a driving range of up to 340 km while returning a combined gas/electric average consumption of 0.6 litres per 100 kilometres. The key here is the reduction in body mass allowed the installation of a smaller and, more importantly, lighter battery without sacrificing driving range. On the flip side the i8, in spite of producing 364 horsepower, sips its fuel at an average rate of 2.5 L/100 km based on the European test cycle.

The unspoken advantage to lightweight construction is the fun factor that comes while reducing the automobile’s burden on the planet. The relative performance of any car is determined by a number of factors, however, the key is the vehicle’s power-to-weight ratio.

Improving this aspect can be accomplished one of two ways. The old method entailed dropping a honking motor into a heavy sled (think Dodge Viper) and relying on brute force to deliver the desired performance. The modern option is to reduce the mass of the car. Replacing heavy steel components with units made from ultra-high-strength steel, aluminum and titanium can reduce weight by anywhere between 10% and 60%. In the longer term, advanced materials such as magnesium and CFRP have the potential to reduce mass by a staggering 50% to 75%.

Simply, shaving mass means the power-to-weight ratio can be increased without having to upsize the engine, which is where the fuel economy and environmental benefits come to the fore. In the end, lightweight construction delivers the best of all worlds.